Process for electrodeposition of compositions containing carbamothioate curing agents

ABSTRACT

An ungelled composition of matter comprising a compound containing groups reactive with isocyanate, a compound containing groups reactive with mercaptan, and a carbamothioate curing agent adapted to generate a plurality of curing units upon being subjected to heating above about critical temperature. The generated curing units contain isocyanate groups, mercaptan groups, or combinations thereof. In preferred embodiments of this invention, the ungelled composition is adapted for use in powder coatings, anodic electrocoating, and cathodic electrocoating.

This is a division of application Ser. No. 812,801, filed July 5, 1977,now U.S. Pat. No. 4,133,916.

The present invention relates to a new composition of matter adaptableto a wide variety of uses.

The ungelled composition of matter disclosed herein comprises:

(A) a compound containing at least about f_(m) groups, each reactivewith an isocyanate group;

(B) a compound containing at least about f_(n) ' groups, each reactivewith a mercaptan group; and

(C) a carbamothioate curing agent adapted to generate a plurality ofcuring units upon being subjected to heating above about criticaltemperature, said curing units containing m isocyanate groups and nmercaptan groups, here m and n are integers each of value of at least 2.

Referring to the curing agent, the carbamothioate (carbamothiolic acidester) curing agent is of linear or branched structure having structuralunits represented by ##STR1## (a carbamothioate group or linkage). Thecarbonylsulfur bond which joins such structural units is heat sensitivewherein such bond is severable at a critical temperature underheat-curing conditions for formation of a plurality of curing units,each having either isocyanate functionality, mercaptan (or thiol)functionality, or combinations of such functionalities. Withoutsubjecting such curing agent to critical heating, the carbamothioate isquite stable and can be utilized and adapted for use in a wide varietyof applications. Thus, in one sense, the curing agent can be thought ofas a masked or blocked isocyanate curing agent wherein a mercaptan orthiol group is the blocking agent; and in another sense, as amercaptan-functional curing agent which is blocked or masked with anisocyanate group. The particular characterization of the curing agent isnot limitative of the present invention as the curing agent is adaptedand designed to release or generate individual curing units under heatcuring conditions wherein some of the curing units have reactiveisocyanate groups and some of the curing units have reactive mercaptangroups for superior performance of the instant curing agent.

Though the sulfur-carbon bond (carbon of the carbonyl group) of thecarbamothioate can be broken by heating to its critical temperature, thecarbamothioate curing agent is quite staple at lower temperatures andcan be utilized in a wide variety of applications, some of which requireheat treating of the composition of matter such as in the formation ofpowder coatings. The curing agent additionally is quite stable whensubjected to the influence of externally applied voltage and, thus, isquite useful in electrocoating applications. The critical temperature(or critical temperature range) at which the sulfur-carbon bond can bebroken broadly can range from about 100° to about 250° C. (heat-curingconditions) and the critical temperature can be pre-determined fairlyprecisely by particular choice of curing agent, compounds (such asresins or polymers) which are combined with the curing agent forcross-linking by the curing agent, and the particular use to which thecomposition is being adapted. For example, highly polar or electronwithdrawing groups attached to the sulfur atom of the curing agent tendto promote breaking of the carbon-sulfur bond at a lower criticaltemperature, whereas rather straight-chained aliphatic groups attachedto the sulfur atom tend to raise such critical temperature for breakingof the bond. Similarly, particular constituent groups attached to thenitrogen atom (which is attached to the carbonyl of the curing agent)will also influence the critical temperature at which the sulfur-carbonbond is broken and the plurality of curing units released. The Exampleswhich follow will further illustrate this point. While not intending tobe bound by theory, the proposed reaction mechanism which is thought tobe involved in the breaking of the sulfur-carbon bond appears to be viaan ionic reaction mechanism wherein the leaving sulfur group acts as aweak base while the nitrogen of the leaving isocyanate-forming groupappears to act as an acid wherein the unshared pair of electrons of theleaving sulfur group are fulfilled by the addition of the hydrogen ofthe nitrogen (formation of a mercaptan) and resulting in the formationof a nitrogen-carbon double bond (formation of an isocyanate group).

In particular applications of the present composition of matter, it canbe fairly critical to precisely control the critical temperature atwhich the curing agent is split apart to yield a plurality of curingunits. For example, in powder coatings applications it is desired thatthe powder coating initially melt and flow to provide good coverage ofthe substrate at a lower temperature followed by curing of the moltencoating at a higher (or critical) temperature. The present curing agentscan be specially designed and adapted to flow at lower temperatures andprovide cure at higher temperatures. In electrocoating adaptations ofthe present composition of matter, the curing agent need only bedispersible in the aqueous electrocoating bath and be adapted tosimultaneously co-deposit with the appropriate cationic or anionicresins, depending upon the particular mode of operation of theelectrocoating process. In these cases, the curing agent advantageouslywill split apart to provide the curing units at lower temperatures foreconomy and efficiency of curing the electrodeposit coating, and needonly be stable in the bath and under the influence of the appliedvoltage in the bath. In other uses of the curing agent of the presentinvention, the particular applications normally will dictate thecritical temperature (or heat curing conditions) to which the curingagent must respond.

Typically, synthesis of the curing agent is routine though moresophisticated techniques often can provide specially designed curingagents especially valuable in particular applications. Generally, thecuring agent is synthesized by the reaction of an isocyanate-functionalcompound with a mercaptan (or thiol) compound in the presence ofappropriate catalysts. Both the isocyanate compound and the mercaptancompound can be multi-functional and can be attached to a monomer,oligomer or polymer. On certain occasions, it is desirable to have thecuring agent attached to one of the resins or polymers whichadditionally comprise the present composition of matter and this can beaccomplished without much difficulty as can be seen by the exampleswhich follow. At least one of such components of the curing agent (theisocyanate compound or the mercaptan compound) must be multifunctionalfor providing cross-linking of the present composition of matter. Also,a few of the isocyanate and/or mercaptan groups may not be fully reactedin synthesizing the present curing agents and it is conceivable thatthese to some degree may pre-react with the compounds combined with thecuring agent under certain conditions, though, this is strictly limitedso that the present composition of matter is ungelled at temperaturesand conditions of less than the critical temperature under heat curingconditions (which are required to fully gel or cross-link the presentcomposition of matter).

The isocyanate compounds useful in formulating the present curing agentscan be aliphatic or aromatic isocyanate compounds and can be in the formof a monomer, oligomer, or polymer. Typical isocyanates include, forexample, toluene diisocyanate, isophorone diisocyanate, ethylene,trimethylene, tetramethylene, pentamethylene, hexamethylene,propylene-1,2, butylene-1,2, butylene-2,3, butylene-1,3, ethylidene andbutylidene diisocyanates; cyclopentylene-1,3, cyclohexylene-1,4, andcyclohexylene-1,2, diisocyanates; m-phenylene, p-phenylene,4,4'-diphenyl, 1,5-naphthalene, and 1,4-naphthalene diisocyanates;4,4'-diphenylene methane, 2,4-tolylene, 4,4'-tolidine, and 1,4-xylylenediisocyanates; dianisidene diisocyanate, 4,4'-diphenyl etherdiisocyanate and chloro-diphenylene diisocyanate; 4,4',4"-triisocyantotriphenyl methane, 1,3,5-triisocyanto benzene, and 2,4,6-triisocyantotoluene; and 4,4'-dimethyl-diphenyl methane 2,2'-5,5'-tetraisocyanate.

Representative mercaptan compounds or thiol compounds useful in thepresent invention include, for example, monododecanethiol,didodecanethiol, dithiophenol, di-para-chlorolthiophenol,dimercaptobenzthiazole, 3,4-dimercaptotoluene, allyl mercaptan,1,6-hexanedithiol, mercaptoacetic acid, benzyl mercaptan, 1-octanethiol,p-thiocresol, 2,3,5,6-tetraflurothiophenol, cyclohexylmercaptan,methylthioglycolate, mercaptopyridines, dithioerythritol,6-ethoxy-2-mercaptobenzothiazole, and the like. Further usefulmercaptans can be found in the 1970-1978 Catalog Handbook of Organic andBiochemicals, catalogue no. 18, Aldrich Chemical Company, Inc.,Milwaukee, Wis.

The curing agent is combined with a compound containing at least aboutf_(m) groups each reactive with an isocyanate group (hereinafterreferred to as compound A). Referring to compound A, such compound canbe a monomer, oligomer, or polymer, depending upon the particular use tobe made of the composition of matter and the performance which thecomposition of mattter should display. Groups which are reactive with anisocyanate group generally are classified as those groups containing alabile hydrogen atom. There should be about f_(m) of such groups whichare adapted to link with the isocyanate-functional curing units of thecuring agent. There are M isocyanate groups formed from the curing agentand there should be about the same number of more labile hydrogenatom-containing groups with respect to the isocyanate groups of thecuring agent. Generally M will range from about 2 to 10 and more oftenfrom about 2 to 5. Compound A can be a polyester, polyether, vinyl,acrylate, polyurethane, polyamine, and similar compounds provided theyhave the requesite functionality reactive with an isocyanate group.Representative groups reactive with an isocyanate group include:alcohols, amines, carboxyl groups, urethanes, ureas, oximes, phenols,enols, silyl amines, and the like.

Compound B contains at least about f_(n) ' groups each reactive with amercaptan group. Compound B, like Compound A, can be a monomer,oligomer, or polymer depending upon the particular application of thecomposition of matter and the performance characteristics desired of thecomposition of matter. There are N mercaptan groups formed from thecuring agent and at least about N groups which are reactive with suchmercaptan group. Generally N will range from about 2 to 10 and moreoften from about 2 to 5. Representative groups which are reactive withthe mercaptan group include unsaturated carbon-carbon groups such astypified by allyls, vinyls, acrylates, acrylamides, ethylenicallyunsaturated dibasic and polybasic acids, (poly)butadienes, and likeunsaturated groups; epoxies; and amine groups which undergo areplacement reaction with the mercaptan group according to the reactionprocedure taught in U.S. Pat. No. 2,417,118, the disclosure of which isexpressly incorporated herein by reference.

It is quite conceivable that a single compound can contain both thereactive groups of Compound A and the reactive groups of Compound B andsynthesis of such compounds generally is quite simple and well known tothose skilled in the art. For example, a single compound containing bothsuch functionalities can be, for example, an unsaturated polyestercontaining hydroxyl groups, a (poly)acrylate containing pendant aminegroups, and similar compounds containing both reactivities. It also canbe useful on occasion to attach the curing agent to at least one of suchcompounds and even to a single compound containing both functionalities.In electrocoating uses of the instant composition of matter, it can behighly advantageous to have the curing agent directly attached to theparticular electrocoating resin so that uniform deposition of the curingagent along with the charged polymer can be practiced. Further on thiswill be found in the examples which follow.

In powder coatings applications of the present invention, compounds (A)and/or (B) are polymers or resins especially adapted to meet thestringent requirements of this field. Powder coatings can be made, forexample, by dispersing the ingredients (compounds (A) and (B) and thecuring agent) in a fugative solvent and spray-drying the resultingdispersion to form a uniform, intimate blend of particles, such as shownin U.S. Pat. No. 3,561,003, incorporated herein by reference.Alternatively, the ingredients can be consolidated into a hot melt andextruded with the extrudate then being ground to powdered form; such asshown in SME Technical Paper No. FC 72-948, presented at the powdercoatings meeting of the Society of Manufacturing Engineers (Cincinnati,Ohio 1972), incorporated herein by reference. Other known ways ofmanufacturing powder coatings can be used advantageously and thefollowing reference is particularly good in teaching the powder coatingart, M. W. Raney, "Powder Coating Technology," Chemical TechnologyReview, No. 45, Notes Data Corporation, Park Ridge, New Jersey (1975),the same incorporated herein by reference.

Nominal particle size of powder coatings ranges from about 30 to about150 microns average diameter and preferably are spherical in geometricalshape. Generally, the powder is applied to a substrate by electrostaticspraying, though other techniques such as fluidized bed operations canbe utilized. Preferably, the powder coating is non-fusible attemperatures of up to about 50° C. so that end-gun or nozzle pluggage isminimized. The applied powder coating is heated for effecting flow-outand good coverage initially without realizing cure or gel of the powdercoating. Typically, the powder coating has a Tg (glass transitiontemperature) of at least about 55° C. and preferably around 60°-95° C.for best performance of the powder coating. With longer times of heatingor at increased temperatures, the flowed-out coating cures to form afully-cured coating on the substrate.

The present carbamothiolic acid ester curing agent is ideally suited topowder coating applications for a variety of reasons including that thecritical temperature of the curing agent can be pre-determined andregulated with good accuracy. The powder coating then can be made tohave the requisite Tg and be substantially non-fusible upon application.Further, the present powder coating can be heated at a temperature belowthe critical temperature (or above the critical temperature for shorttimes of heating) to effect good flow-out and coverage. Also, there arevirtually no volatiles emitted from the curing agent during heat-curingoperations for better performance of the coating and reduced pollutionemission problems.

In anodic electrocoating applications of the present composition,compounds (A) and/or (B) preferably are polymers or resins especiallyadapted for use in this field. Such compounds are made to be anionic(negatively charged) so that during electrodeposition operations, suchcompounds will migrate to the anode and be deposited therein. It shouldbe understood, though, that of compound A, compound B, or thecarbamothioate curing agent, only one of these need be charged and theothers will be carried to the anode by the charged species as is wellknown in this art. Typically, such compounds are made anionic byproviding a multiplicity of carboxyl groups on the compounds. Theanionic compounds are dispersed in the electrocoating bath by adding anamino-compound thereto to provide negatively charged functionality fromthe carboxyl groups of the compound. Suitable amino-compounds, forexample, include monoethanol amine, diethanol amine, triethano amine,monoethyl amine, diisopropyl amine, trimethylamine, cyclohexylamine, andthe like and mixtures thereof.

The anodic electrocoating composition is dispersed in the electrocoatingbath at about 5 to about 20% non-volatiles solids at about 15° to 50° C.The anode substrate then is immersed in the bath while an electricpotential is maintained therethrough. Electric potential often rangebetween about 20 and 500 volts, with about 50 to 300 volts beingpreferred. In order to maintain the ratio of anodic polymer to curingagent fairly constant, it can be advantageous to have the curing agentdirectly attached to the anodic polymer (or one of them if there are twoor more anodic polymers in the bath) so that uniform deposition on theanode substrate is maintained. Further on practice of anodicelectrocoating can be found in Advances in Electrophoretic Painting1971-1972, R. H. Chandler Limited (May 1973).

In cathodic electrocoating applications of the present composition,compounds (A) and/or (B) are polymers or resins especially adapted foruse in this field. Such compounds are made to the cationic so thatduring electrodeposition they will migrate to the cathode substrate andbe deposited thereon. Of course, only one compound (A or B) or thecuring agent need be charged. Suitable cationic functionality can beprovided in the form of onium groups such as sulfonium groups,phosphonium groups, ammonium group (quaternary ammonium group); and fromamine groups suitably protonated with a proton-denoting acid. Further onthis can be found in Advances in Electrophoretic Painting 1973-1974 -Cathodic Electropainting, R. H. Chandler Limited (March 1975).

The cationic polymer and curing agent are dispersed in theelectrocoating bath at about 5% to about 20% non-volatiles solids atabout 15° to 50° C. An electric potential of about 20 to 500 volts ismaintained therethrough for deposition of the cathodic composition ontothe cathode substrate. As mentioned for aniodic electrocoating, it canbe similarly advantageous to directly attach the curing agent to thecathodic polymer.

Of course the present composition can be dispersed in an aqueous solventfor conventional application, such as, for example, brushing, rolling,dipping, spraying and the like. In these cases, it can be useful toformulate the coating composition to contain a very high non-volatilessolids content of about 60 to 90% or higher. This can be readilyaccomplished as the Examples will demonstrate. Similarly, a fugativeorganic solvent can be used also. Additional uses for the presentcomposition include, for example, laminates, molding compounds, and thelike.

A decided benefit of the present composition in any use is that bothisocyanate and mercaptan functionalities from the curing agentparticipate in cure of the composition. High performance of urethanebonds is well known and such bonds (or urethane-type bond such as a ureaor the like) are formed from the isocyanate curing units. Of unexpectedbenefit is the unusually good contribution that the mercaptan curingunits provide to the present composition. One benefit is the superiorcorrosion-inhibition which the mercaptan curing linkages exhibit in thepresent curable composition. Most conventional isocyanate blockinggroups are volatile and are readily volatilized during heat curingoperations (e.g. caprolactams), though with special care, someisocyanate blocking groups may be designed to remain in the cured filmor even link into the film on rare occasion. The unusualcorrosion-protection afforded in the present invention can be seen inthe following Example XVII below.

PREPARATION OF CURING AGENTS EXAMPLE I

To a solution of 17.4 grams of toluene diisocyanate (0.1 mole) and 50milliliters of toluene, 20.8 grams of dodecanethiol (0.1 mole)containing 0.1% triethylamine catalyst was added slowly over a 12 hourperiod at room temperature followed by heating at 50° C. for threehours. The resulting monododecanethioltoluene diisocyanate curing agentwas analyzed and found to contain 7% free isocyanate (calculated valueis 11% free isocyanate). The presence of some free isocyanate wasconfirmed by infrared spectroscopy.

EXAMPLE II

Into a flask was placed 42.8 grams of dodecane thiol (0.2 moles), 0.1%triethylamine catalyst, and 100 milliliters of toluene. The reactionmixture was maintained at room temperature under slow stirring and 17.4grams of toluene diisocyanate (0.1 mole) was added dropwise thereto.After the addition of the toluene diisocyanate, the mixture wascontinued to be stirred for an additional 12 hours followed by heatingat 80° C. for three hours until all of the isocyanate was determined tohave been reacted. The mixture then was cooled and washed with 50milliliters of heptane to extract 52 grams of precipitate. Theprecipitate contained 91% of the desired didodecanethiol-toluenediisocyanate curing agent. The curing agent was determined to have amelting point of 89°-90° C.

EXAMPLE III

The procedure of Example II was repeated except that the TDI was addedto a mixture of dithiolphenol dispersed in chloroform and containingDABCO amine catalyst (DABCO is a registered trademark of AmericanCyanamide Company). The resulting precipitate was found to contain 80%of the desired dithiolphenol-toluene diisocyanate curing agent. Thiscuring agent was determined to have a melting point of 140°-145° C.

EXAMPLE IV

The procedure of Example III was repeated except thatdi-parachlorothiolphenol was used instead of dithiolphenol. Theprecipitate yielded 88% of the di-para-chlorothiolphenol-toluenediisocyanate curing agent. This curing agent had a melting point of 178°C.

EXAMPLE V

The reaction procedure of Example III was repeated except that thedithiolphenol was replaced with dimercaptobenzothiozole and thechloroform solvent was replaced with toluene solvent. The resultingprecipitate was found to contain the desireddimercaptobenzothiozole-toluene diisocyanate curing agent.

EXAMPLE VI

The curing agent was made by the reaction of 0.03 moles of3,4-dimercaptotoluene, 0.01 moles of para-chlorothiolphenol, and 0.04moles of toluene diisocyanate dispersed in methylethylketone solvent inthe presence of 0.1% dibutyltin dilaurate catalyst. The ingredients wereheated at about 80°-100° C. until it was determined that no freeisocyanate remained in the reaction mixture. The resulting curing agentcan be represented conventionally by the following structure: ##STR2##

EXAMPLE VII

The reaction procedure of Example VI was repeated except that thereaction mixture contained 1 mole of toluene diisocyanate and 2 moles ofparachlorothiolphenol.

POWDER COATINGS/SOLVENTLESS BLENDS EMBODIMENT

In Examples VIII through XIII, the curing agent, compound A, andcompound B were placed in aluminum cups, heated to about 160° C., andthe curing time recorded (i.e. time at which the composition gelled orcured). The results for these Examples are recorded in Table I below.

In Example XIV, powder coating formulated had the curing agent reactedonto compound A. Compound B then was separately combined with thecompound A-curing agent adduct. In Example XV, the powder coating hadthe curing agent and both compounds A and B reacted into a singlemolecule.

                                      TABLE I                                     __________________________________________________________________________           Curing Agent                                                                         Compound A  Compound B                                                                             Gel Time                                   EXAMPLE                                                                              (wt in gms)                                                                          (wt in gms) (wt in gms)                                                                            (min)                                      __________________________________________________________________________    VIII   Ex. II (1) hydroxy-terminated                                                                    (2) polybutadiene                                          (3 gms)                                                                              polybutadiene                                                                             (12 gms)                                                          (12 gms)             2-5                                        IX     Ex. VII                                                                              (3) trihydroxypolyether                                                                   (2) polybutadiene                                          (5 gms)                                                                              (5 gms)     (0.1 gms)                                                                              9                                          X      Ex. VII                                                                              (4) epoxy resin-dieth-                                                                    (5) unsaturated                                            (8 gms)                                                                              anol amine adduct                                                                         polyester                                                         (6 gms)     (8 gms)  3                                          XI     Ex. VII                                                                              (3) trihydroxypolyether                                                                   (2) polybutadiene                                          (8 gms)                                                                              (3 gms)     (2 gms)  20                                         XII    Ex. VII                                                                              (6) styrene-allylalcohol                                                                  (2) polybutadiene                                          (4 gms)                                                                              (4 gms)     (2 gms)  15                                         XIII   Ex. VII                                                                              (4) epoxy resin-                                                                          (7) epoxy resin                                            (2 gms)                                                                              diethanolamine added                                                                      (1.7 gms)                                                         (1 gm)               4                                          __________________________________________________________________________     (1) R15M, a liquid hydroxyterminated polybutadiene, MW of 3000-3500,          hydroxy content of 0.80 meg./gm, hydroxy no. 45 (mg. of KOH), ARCO Corp.,     Sinclair Petrochemicals Division.                                             (2) Lithene QH liquid polybutadiene, MW of 3100, Lithium Corp. of America     Bessemer City, North Carolina.                                                (3) Liquid trihydroxypolyether being the reaction product of 1 mole of        trimethylolpropane and 7 moles of propylene oxide (BF.sub.3 etherate          catalyst).                                                                    (4) Reaction product of 1 mole of an epoxy resin (DER 332 epoxy resin,        epoxy equivalent of 172-196, Dow Chemical Company, Midland, Michigan) and     1 mole of diethanol amine                                                     (5) Unsaturated polyester resin made by the fusion cook at 230° C.     of 1 mole of trimethylolpropane, 2 moles of triethylene glycol, 1 mole of     1,6hexane diol, and 3 moles of maleic anhydride.                              (6) RS100 styrene/allyl alcohol copolymer, MW of 1200-1700, Monsanto          Chemical Corp.                                                                (7) DER 332 epoxy resin, epoxy equivalent of 172-196, Dow Chemical            Company, Midland, Michigan.                                              

EXAMPLE XIV

The curing agent was prepared by the dropwise addition of 1.1 moles ofpara-chlorothiophenol dispersed in dry methylethylketone solvent to aflask containing one mole of toluene diisocyanate and 0.1% triethylaminecatalyst dispersed in dry MEK solvent. The reaction mixture was held atroom temperature until the free isocyanate content was determined toabout 5-6%.

The curing agent (130 gms, 70% nonvolatiles in MEK) was added to thestyrene-allyl alcohol copolymer of Example XII (200 gms) at roomtemperature. This reaction mixture then was heated at 40° C. for 3 hoursat which time it was determined that no free NCO groups remained in thereaction mixture. The copolymer-curing agent product precipitated fromsolution as a fine powder. The powder was recovered from the solutionand dried.

The dried powder (0.2 gms) was blended with 10 grams of a soliddiacetone acrylamide, the blend placed in an aluminum cup andheat-cured. The cured material had no mercaptan odor indicating that ithad fully cured.

EXAMPLE XV

The following ingredients were reacted in substantially the same manneras described in Example XIV: 70 grams of a p-chlorothiophenol--TDIadduct (1:1 molar ratio), 60 grams of a hydroxyethylacrylate--TDI adduct(1:1 molar ratio), and 100 grams of the RJ-100 styrene-allyl alcoholcopolymer of Example XII.

The powder recovered from the reaction mixture was placed in an aluminumcup and heated to fully cure the powder.

EXAMPLE XVI

The curing agent of Example VI (30 gms) and 100 gms an epoxy resin (DER664, MW of 1800), epoxy equivalent of 900, Dow Epoxy Resin, Dow ChemicalCompany) were dispersed in MEK solvent. The solvent was evaporated toyield a uniform solids mixture. This powder was applied to a steel paneland baked at about 205° C. for ten minutes to yield a fully-curedsolvent-resistant film on the panel.

ANODIC ELECTROCOATING EMBODIMENT EXAMPLE XVII

An anodic electrocoating resin was prepared by the solutionpolymerization of methylmethacrylate (290 parts), ethyl acrylate (230parts), butylacrylate (320) parts), hydroxyethylacrylate (400 parts),and methacrylic acid (60 parts) dispersed in 600 parts of a2-butoxy-ethanol-1 solvent. The curing agent was formulated from onemole of a 3,4-di-mercaptotoluene/TDI adduct (1:2 mole ratio) reactedwith 2 moles of para-chlorothiophenol in accordance with the procedureof Example VI. Compound B was a 1:1 weight ratio mixture of a ciacrylateof an epoxy resin (2 moles of acrylic acid reacted with 1 mole of theDER 332 epoxy resin of Example XIII) and melamine acrylate (2.7 acrylatefunctionality).

To the anodic resin was blended 20% by weight of the curing agent and20% by weight of the epoxy acrylate/melamine acrylate resinous mixture.The blend was neutralized with triethanolamine and dispersed indeionized water to form an electrocoating bath of 10% non-volatilesolids dispersion. The anodic electrocoating composition then wasanodically electrodeposited onto a steel panel at 100-200 volts for60-90 seconds. The coated panel was removed from the bath, washed withwater, and baked in an oven at 205° C. for 20 minutes. After baking, afully-cured solvent-resistant film covered the panel.

EXAMPLE XVIII

The procedure of Example XVII was repeated except that thehydroxyethylacrylate in the anodic resin was replaced withglycidylmethacrylate to provide an oxirane-functional anodic resin.

EXAMPLE XIX

The procedure of Example VII was repeated except that thehydroxyethylacrylate in the anodic resin was replaced with methacrylicacid and the resulting anodic resin was reacted further withglycidylacrylate to provide an acrylate-functional anodic resin.

CATHODIC ELECTROCOATING EMBODIMENT EXAMPLE XX

In 2-butoxy-ethanol-1, one mole of an epoxy resin (DER 664) was reactedwith one mole of diethanolamine to form an amino-epoxy resin adduct.This adduct was blended with 20% by weight of the curing agent ofExample XVII and 10% by weight of N,N'-para-phenylenedimaleimide. Thisblend was acidified with acetic acid and added to water to form anelectrocoating bath of 8% non-volatiles solids dispersion.

A steel panel was cathodically electrocoated with the cathodicelectrocoating composition at 100 volts for minutes, removed from thebath, and washed with water to remove any excess coating. The coatedpanel then was baked at 205° C. for 30 minutes to provide a fully-cured,solvent-resistance film on the panel.

EXAMPLE XXI

The cathodic resin was prepared from one mole of methylethanolaminereacted with one mole of an epoxy resin (DER 664) in 2-butoxy-ethanol-1.The cathodic resin was blended with 20% by weight of the curing agent ofExample VII. The blend was acidified with acetic acid and let down inwater to form an electrocoating bath of 8% non-volatiles solidsdispersion.

A steel panel was cathodically electrocoated with the composition andbaked at 205° C. for 30 minutes. This resulted in a fully-cured, solventresistant film on the panel.

EXAMPLE XXII

A sulfonium ion copolymer was made by copolymerizing vinyl benzylsulfonium monomer (1 mole of the reaction product of 1 mole ofvinylbenzylchloride with 1 mole of dimethylsulfide),hydroxyethylacrylate (1 mole), butylacrylate (2 moles), and styrene (1mole). This copolymer was blended with 30% by weight of the curing agentof Example XVII and 30% by weight of melamine acrylate (2.7 acrylatefunctionality).

The blend was dispersed in water to form an 8% non-volatiles solidsdispersion and cathodically electrodeposited onto a steel panel. Thecoated panel was baked at 205° C. for 30 minutes to produce afully-cured film on the panel.

EXAMPLE XXIII

A hydroxyl-rich polyester was formulated by the reaction of two moles ofsuccinic anhydride with two moles of propylene glycol and one mole ofthiodiethenol followed by the addition of an excess (based on thehydroxyl content of the polyester resin) of 3-mercaptopropionic acid.The resulting mercaptan-terminated polyester resin then was reacted witha carbamothioate curing agent which was the reaction product of 1 moleof 3,4-dimercapto-toluene, 2 moles of TDI, and 1 mole ofparachlorothiophenol (prepared according to the procedure of ExampleVI). One hundred grams of the curing agent-containing cathodic resinthen was acidified with 1 mole of acetic acid and 1 mole of methyliodideand blended with 30 grams of a 1:1 weight ratio mixture of melamineacrylate (2.7 acrylate functionality)/epoxy acrylate resin of ExampleXVII. This blend was dispersed in deionized water to form an 8%nonvolatiles dispersion (electrocoating bath).

A steel panel was immersed in the bath as the cathode and theelectrocoating composition electrodeposited thereon at 60 volts for 2minutes. The coated panel was removed from the bath, washed with water,and baked at 205° C. for 30 minutes. A solvent-resistant coating with nomercaptan odor covered the panel indicating that full curing had takenplace.

EXAMPLE XXIV

One mole of the DER 664 epoxy resin of Example XVI was reacted with onemole of nonyl phenol in 2-butoxy-ethanol-1 solvent (20% non-volatilessolution) in the presence of 0.5% of benzyldimethylamine catalyst,followed by a further reaction with the reaction product of one mole ofbutylthioethanol and one mole of TDI. Next, one mole oftrimethylolpropane tri-(beta-mercaptopropionate) was added to form amercaptan-functional, urethane-modified epoxy resin. The curing agentthen was attached to the epoxy resin by the addition of a thiophenol-TDIadduct (1:1 molar ratio) thereto.

This resin was slightly acidified with acetic acid and 1 mole ofmethyliodide, blended with 30% by weight of a 1:1 weight ratio mixtureof DER 332 epoxy resin and pentaerythritol triacrylate, and dispersed inwater to form an 8% non-volatile electrocoating bath. A steel panel wascoated and cured in a manner similar to that described in Example XXIII.

EXAMPLE XXV

Two moles of TDI was reacted with 0.75 moles of poly-(tetra-methyleneether glycol), having a molecular weight of 2,000, and 0.25 moles ofthiodiethanol, followed by a further reaction with one mole of propanol.This adduct was reacted with one mole of the triester of3-mercaptopropionic acid with trimethylolpropane to produce amercaptan-terminated urethane resin. This urethane resin had the curingagent reacted onto it by the addition of TDI/para-chlorothiophenol (1:1molar ratio) curing agent adduct to the urethane resin. One hundredgrams of the curing agent-modified urethane resin was neutralized withacetic acid and 0.25 moles of methyl iodide and blended with 20 grams ofa 1:1 weight ratio mixture of triacrylamido-s-triazine and thediacrylate of DER 332 epoxy resin of Example XVII. The blend then wasadded to water to form an 8% non volatiles dispersion.

The electrocoating composition was cathodically electrodeposited ontosteel panels in a manner similar to the previous Examples, washed withwater, and baked at 205° C. for 25 minutes to yield a fully-curedcoating on the panels.

EXAMPLE XXVI

A butylthioethylacrylate copolymer was synthesized by the solutionpolymerization of one mole of butyl acrylate, one mole ofmethylmethacrylate and one-half mole of the reaction products ofbutylthioethanol esterified with ethylacrylate, under standard solutionpolymerization conditions in 2-butoxy-ethanol-1 solvent and using onemole of thiolacetic acid as a chain transfer agent. The copolymer washydrolyzed with acetic acid to convert the thiolacetic ester linkagesinto mercaptan groups. The curing agent of the previous Example then wasreacted onto the copolymer.

The cathodic resin containing the curing agent was acidified with aceticacid and methyliodide, blended with triacrylamido-s-triazine, let downin water, and electrocoated onto steel panels in a manner similar to theprevious Examples. Upon baking, a fully-cured coating with no mercaptanodor covered such panel.

DEMONSTRATION OF CORROSION-INHIBITION EXAMPLE XXVII

The following four compositions were formulated for testing theircorrosion-inhibiting properties.

A. Control A was a hydroxy-epoxy resin (DER 664 epoxy resin of ExampleXVI) used as a standard for this series of tests.

B. The reaction product of Control A and 2 moles of phenol and such isdesigned to simulate a coating wherein a phenol blocking agent wouldlink into the coating.

C. The reaction product of Control A with 2 moles of thiophenol.

D. The reaction product of Control A with 2 moles of dodecylmercaptan.

Each of the foregoing compositions was dissolved in chloroform (10-20%solids) and steel panels dipped therein. The coated panels were airdried to yield continuous 1-2 mil thick coatings on the panels. A scribewas cut into the face of each of the coated panels and the scribedpanels placed into a 5% NaCl salt solution for 48 hours(ASTM-D-1654-61). After the salt bath was completed, each panel wasexamined in order to determine the amount and severity of rusting thathad taken place.

The panel coated with the coating of Control A was severely rusted inthe scribe and also was severely rusted over the entire face of thepanel. The panel with the coating of composition B showed severeundercutting or rust migration from the scribe underneath the coatingand down the grain of the metal panel. The panel coated with thealiphatic mercaptan coating of composition D had moderate rust in thescribe and only slight rust undercutting. The panel coated with thearomatic mercaptan coating of composition C showed only a few smallpatches of rust in the scribe and no signs of rust undercutting.

The foregoing results clearly demonstrate the unexpectedly superiorcorrosion-protection which the mercaptan linkages formed from thecarbamothioate curing agent contribute to the compounds of the presentinvention. Such corrosion protection can be particularly valuable inpowder coatings and anodic electrocoatings uses of the presentinvention.

What is claimed is:
 1. An electrocoating process for coating a substratewith an electrocoating composition dispersed in an aqueouselectrocoating bath, which comprises:electrodepositing saidelectrocoating composition onto said substrate, said compositioncomprising: a compound A containing at least about two functional groupseach reactive with an isocyanate group, a compound B containing at leastabout two functional groups each reactive with a mercaptan group, and acarbamothioate curing agent adapted to generate a plurality of curingunits upon being heated to above about critical temperature, said curingunits containing at least two isocyanate groups and at least twomercaptan groups with at least one of said curing units containing atleast two of said groups; and heating said coated substrate to atemperature above about said critical temperature to generate saidplurality of curing units to cure said coating.
 2. The electrocoatingprocess of claim 1 wherein said substrate is an anode substrate and saidcomposition is anodically electrodeposited onto said anode substrate. 3.The electrocoating process of claim 1 wherein said substrate is acathode substrate and said composition is cathodically electrodepositedonto said cathode substrate.
 4. The electrocoating process of claim 1wherein said critical temperature is between about 100° and 250° C. 5.The electrocoating process of claim 1 wherein compound A and compound Bare the same compound.
 6. The electrocoating process of claim 1 whereinsaid curing agent is attached to compound A.
 7. The electrocoatingprocess of claim 1 wherein said curing unit is attached to compound B.8. The electrocoating process of claim 5 wherein said curing agent isattached to said same compound.
 9. The electrocoating process of claim 1wherein at least one of said curing units contains at least 2 isocyanategroups and at least one of said curing units contains at least 2mercaptan groups.